In the field of analytical chemistry, the demand for direct sampling under ambient conditions has increased, and this has led to the development of a variety of ambient ionization sources. Ambient ionization sources ionize analytes in the respective ambient environment (in-situ) with no intrinsic requirement for sample preparation. This advantage allows real-time, on-site detection, saving time and resources.
Electrospray based ambient ionization sources offer significant potential benefits over traditional vacuum based analytical techniques. In particular, desorption electrospray ionization (DESI) allows the examination of analytes directly from ambient surfaces, eliminating the requirement for sample preparation prior to analysis (Takats, Z.; Wiseman, J. M.; Gologan, B.; Cooks, R. G., Science 2004, 306, 471-473). DESI desorbs and ionizes compounds from surfaces by directing a pneumatically assisted electrospray at the surface of interest. Extractive electrospray ionization (EESI) has been shown to allow the analysis of liquid samples such as undiluted milk, urine, and other complex mixtures without sample preparation (Chen, H.; Venter, A.; Cooks, R. G., Chemical Communications 2006, 2042-2044). Electrospray-assisted laser desorption/ionization (ELDI) combines laser desorption with post-ionization by electrospray and has been applied to the rapid analysis of solids (Shiea, J.; Huang, M.-Z.; HSu, H.-J.; Lee, C.-Y.; Yuan, C.-H.; Beech, I.; Sunner, J., Rapid Communications in Mass Spectrometry 2005, 19, 3701-3704).
A problem with the above electrospray based ambient ionization sources is the requirement of an electrospray solvent and high velocity auxiliary gas flow, or additional laser device, for operation of the sources. The need for a continuous supply of solvents and gases, as well as the associated containers and disposal services, makes electrospray based methods less than ideal for in situ applications.
There is an unmet need for more simpler ambient ionization sources which do not require expendables like solvents, and methods of using these sources to analyze sample materials.